Ecotoxicological Effects of Silver Nanoparticles (Ag-NPs) on Parturition Time, Survival Rate, Reproductive Success and Blood Parameters of Adult Common Molly (Poecilia sphenops) and Their Larvae

Nanoparticles (NPs) can display toxicological effects on aquatic organisms. This study investigates ecotoxicological effects of Ag-NPs on reproductive and blood parameters of adult common molly (Poecilia sphenops) and their larvae. During the LC50 96 h test, female fish were exposed to concentrations of 0, 5, 15, 25, 35, 45 and 60 mg L−1 of Ag-NPs, while larvae were exposed to 0, 3, 5, 10 and 15 mg L−1. Finally, we aim to evaluate the effects of 0, 5, 10 and 15 mg L−1 of Ag-NPs on parturition time, reproductive success and hematological parameters of the mature fish exposed to sub-lethal concentration during a 62-day period. We also evaluated the survival rate of larvae. The results show a positive correlation between mortality rate and Ag-NP concentration. Values for LC50 96 h in adult fish and larvae were 26.85 mg L−1 and 6.22 mg L−1, respectively. A lack of parturition and reproductive success were seen in fish that underwent chronic exposure to Ag-NPs (15 mg L−1). The results show that RBC, WBC and hematocrit were significantly decreased in fish exposed to Ag-NPs. In addition, the serum concentrations of total protein, albumin, cholesterol and triglycerides were significantly increased in fish submitted to Ag-NPs (concentrations of 5–15). In conclusion, submitting a fish to higher concentration than 10 mg L−1 has adverse effects on reproductive system and blood parameters.

​Study of the Zootechnical Performance of Tilapia cabrae and Oreochromis schwebischi in a Controlled Environment: The Case of the Mbolet Fish Farm in Lambaréné, Gabon

Background: The study of the zootechnical performance of Tilapia cabrae and Oreochromis schwebischi was carried out at the Mbolet fish farm in Lambaréné in Gabon in order to evaluate the growth and reproductive performance of these two species. Methods: For this purpose, 226 fish (113 of T. cabrae with an average weight of 30.55±9.5 g and 113 O. schwebischi with an average weight of 20.64±10.5 g), were distributed in four 6 m2 tanks with two replicates per species for the growing phase which lasted 60 days. For the reproductive phase, 42 selected mature fish, including 6 males and 36 females of each species, were placed in six 2 m2 ponds with three replicates per species for 78 days. Result: The survival rate, the number of reproductions per species and the absolute, relative and system productivities were determined. It was found that the average weight gain, daily individual growth and specific growth rate were significantly (p less than 0.05) higher in T. cabrae, 48.1±5.51 g, 0.8±0.092 g/day and 1.57±0.066% g/day respectively, than in O. schwebischi, 27.11±9.23 g, 0.45±0.15 g/day and 1.38±0.051% g/day respectively. At the end of reproduction, the absolute productivity of T. cabrae (234.75±24.71 larvae/female/egg-laying) was significantly higher (p less than 0.05) than that of O. schwebichi (104.68±46.64 larvae/female/laying). System productivity was significantly higher (p less than 0.05) in O. schwebichi (11.34±2.29 larvae/m2/day) compared to that of T. cabrae (4.12±1.73 larvae/m2/day). Thus, on a fish farm, the use of these species may be possible.

The First Record of Adult Spotted Sea Bass (Lateolabrax maculatus, McClelland, 1844) from the Coastal Waters of Quang Ninh Province, Vietnam

Spotted sea bass (Lateolabrax maculatus, McClelland, 1844) is a species belonging to the genus Lateolabrax (Lateolabracidae), and is characterized by the many distinct black spots on the bodies of mature fish. For the first time, six specimens have been recorded in Quang Ninh province. The specimens were collected from Luon Cave in Bai Tu Long National Park in May-June 2019. The new specimens collected from Quang Ninh, Vietnam are different from the recorded specimens from Japan, Korea, Taiwan, and China in terms of lateral line scales (LLS) as the samples collected in Quang Ninh, Vietnam have 94-97 scales and the samples collected from the other countries have 66-82 scales. Phylogenetic analysis of the 16S rDNA sequence confirmed that all of the samples collected in Quang Ninh, Vietnam belonged to the species of spotted sea bass.

Eradication of the Invasive Common Carp, Cyprinus carpio from a Large Lake: Lessons and Insights from the Tasmanian Experience

Common carp (Cyprinus carpio, L. 1758) are the most abundant pest fish species in Australia, detrimental to ecosystem integrity and values, and in need of suitable management solutions. In January 1995, this destructive pest was discovered in two large, connected Tasmanian lakes—Lakes Crescent (23 km2) and Sorell (54 km2). After an initial assessment, carp were immediately contained to these waters using screens to prevent their escape down-stream, followed by swift legislation to enforce closure of the lakes to the public. Assessment and evaluation of carp numbers occurred throughout the eradication program, with effort focused on Lake Crescent. Beginning with undirected removal, techniques progressively evolved to more sophisticated targeted removal with assistance from biotelemetry, in conjunction with gill netting and electro-fishing. Real-time population estimates and in situ observations resulted in a detailed cumulative understanding of carp population dynamics, behaviour and seasonal habitat choice. This allowed strategic deployment of fences to block access to marshes, and the installation of steel traps within the fences. These gears specifically prevented spawning opportunities, while concurrently capturing mature fish. Following 12 years of adaptive and integrated effort, 7797 carp (fry, juvenile and adult) were captured from Lake Crescent, with the last carp being caught in December 2007. The subsequent 14 years of monitoring has not resulted in the capture of any carp, confirming the successful eradication of carp from Lake Crescent. These management practices have been successfully replicated in the larger Lake Sorell, where 41,499 carp (fry, juvenile and adult) have been removed. It is now estimated that there are few, if any carp remaining. Collectively, the techniques and strategies described here were reliable, and can be applied as a model to control or eradicate pest populations of carp in freshwater lakes elsewhere.

LENGTH-WEIGHT STRUCTURES AND FECUNDITY OF ANADROMOUS MASU SALMON (ONCORHYNCHUS MASOU) FROM WESTERN KAMCHATKA

Masu salmon Oncorhynchus masou is the most thermophilic species among the Pacific salmon, and Kamchat-ka peninsula is the northern border of its distribution. Due to small abundance, the biology of this species on the peninsula is poorly studied. Regular scientific researches of Masu salmon in Kamchatka have been con-ducted since 2009. The length-weight structures and fecundity of mature Masu salmon have been analyzed in several streams on western Kamchatka over a 10-year period (from 2009 to 2018) and present time. It has been established that the length, weight and fecundity of mature fish are different in the rivers of the peninsula. A tendency of increasing the biological characteristic of the species in recent years has been noted.

Changes in age and maturity of anadromous whitefish (Coregonus lavaretus) in the northern Baltic Sea from 1998 to 2014

The maturation of anadromous whitefish (Coregonus lavaretus) was analysed from samples taken from commercial coastal fishing in 1998–2014 in the Gulf of Bothnia. Whitefish matured at a younger age from year to year. The proportion of older (5–12 sea years) mature males decreased from 79% to 39% in the northern Gulf of Bothnia (66°N–64°N) and from 76% to 14% in southern (64°N–60°30'N) during the study period. At the same time, the proportion of young males (2–4 sea years) increased. Whitefish matured younger: the proportion of mature fish at age four increased in both the north and south among females (13% → 98%; 6% → 85%) and males (68% → 99%; 29% → 89%). The catch length of four-year-old fish increased during the study period in both sexes. In contrast, the length of six-year-old females decreased from year to year. Sea surface temperatures increased during the study period, and were possibly associated with a decrease in the age of maturation and faster growth.

Sakhalin sturgeon Acipenser mikadoi (Acipenseridae): results of study and proposed measures for conservation of the species

All available data on sakhalin sturgeon Acipenser mikadoi are summarized. Its historical and modern habitats are described and their significant reduction is noted. Now the species is abundant in the Russian part of its range only — in the Tumnin River, where it is represented in commercial catches by two clearly different groups: large-sized juveniles (FL 43–68 cm) and mature fish (FL 135–169 cm). Juveniles of sakhalin sturgeon migrate during their first years, as their osmoregulatory system forms, to the lower reaches of Tumnin, to the internal estuary, and then to the Datta Bay, the Tatar Strait and the Japan Sea. When returned to the Tumnin, the spawners of sakhalin sturgeon have the length 135–169 cm (n = 29) and weight 15–36 kg. Sex ratio among the caught mature fish is 13.0 : 4 or 3.2 : 1 for females : males, on average. Fecundity of the sturgeon females sampled for artificial reproduction varied from 44.8 to 150.0 thousand eggs, on average 87.3 ± 12.1 . 103 eggs. In total, 17 mature spawners of A.mikadoi were caught in the Tumnin River in 2006–2019 for artificial reproduction (♀ = 13, ♂ = 4), 13 individuals were injected, among them 4/5 of females and 2/3 of males gave high-quality sex products. Producers of this species were distinguished by high survival during manipulations of fish breeding (100 %). Their progeny had low survival, both embryos during incubation and juveniles during rearing; the survival rate for the stage from eggs laid for incubation to juveniles with weight 3.4–7.0 g was 1.85 %. The low survival was supposedly reasoned by combination of unfavorable environmental factors and fish-breeding manipulations. Totally 11,214 juveniles of sakhalin sturgeon with weight from 3.4 to 7.0 g were released into the natural habitat (Tumnin river) in 2007, 2008, 2015, 2017, and 2019. At Anyui sturgeon fish hatchery, the broodstock of sakhalin sturgeon with 274 individuals of 5 ages is created and operated successfully. The male sturgeons in the hatchery mature at the age of 8 years. Here, 11 males of the 2007–2008 year-classes participated in the spawning in 2015–2019. Re-maturation of males was not recorded yet. For the broodstock formation in other fish hatcheries, 200 juveniles of sakhalin sturgeon were transferred to them. To preserve the species, a set of measures is proposed to strengthen its protection and to enhance its artificial reproduction, including the fry releasing into the rivers of the mainland coast, Sakhalin Island, and Japan.

Adaptation of the carbamoyl-phosphate synthetase enzyme in an extremophile fish

Tetrapods and fish have adapted distinct carbamoyl-phosphate synthase (CPS) enzymes to initiate the ornithine urea cycle during the detoxification of nitrogenous wastes. We report evidence that in the ureotelic subgenus of extremophile fish Oreochromis Alcolapia , CPS III has undergone convergent evolution and adapted its substrate affinity to ammonia, which is typical of terrestrial vertebrate CPS I. Unusually, unlike in other vertebrates, the expression of CPS III in Alcolapia is localized to the skeletal muscle and is activated in the myogenic lineage during early embryonic development with expression remaining in mature fish. We propose that adaptation in Alcolapia included both convergent evolution of CPS function to that of terrestrial vertebrates, as well as changes in development mechanisms redirecting CPS III gene expression to the skeletal muscle.

Influence of nutrient enrichment on the growth, recruitment and trophic ecology of a highly invasive freshwater fish

The establishment probability of introduced alien fish can be context dependent, varying according to factors including propagule pressure and biotic resistance. The influence of nutrient enrichment on establishment outcomes of alien fishes is uncertain, yet this is a common anthropogenic stressor of many freshwaters. Here, the small-bodied alien topmouth gudgeon Pseudorasbora parva was used in mesocosms to experimentally test how a gradient of nutrient enrichment affected their growth rates, recruitment and trophic ecology. A ‘Control’ represented ambient, mesotrophic conditions, while treatments covered three levels of nutrient enrichment: low (eutrophic), medium (hypertrophic) and high (very hypertrophic). Each mesocosm was seeded with 6 mature P. parva (equal sex ratio) at the start of their reproductive season. After 100 days, length increments of the adult fish were significantly elevated in the low treatment, and these fish had also produced significantly higher numbers of 0+ fish compared to all other treatments. The trophic niche width of the mature fish was substantially higher in the control than the treatments, but this did not appear to confer any advantages to them in somatic growth rate or reproductive output. These results suggest that the nutrient status of receiving waters can have substantial impacts on the outcomes of fish introductions, where eutrophic conditions can assist the rapid population establishment of some alien species.

Myomixer is expressed during embryonic and post-larval hyperplasia, muscle regeneration and fusion of myoblats in rainbow trout (Oncorhynchus mykiss)

1.AbstractIn contrast to mice or zebrafish, trout exhibits post-larval muscle growth through hypertrophy and formation of new myofibers (hyperplasia). The muscle fibers are formed by the fusion of mononucleated cells (myoblasts) regulated by several muscle-specific proteins such as myomaker or myomixer. In this work, we identified a unique gene encoding a myomixer protein of 77 amino acids (aa) in the trout genome. Sequence analysis and phylogenetic tree, showed moderate conservation of the overall protein sequence across teleost fish (61% of aa identity between trout and zebrafish myomixer sequences). Nevertheless, the functionally essential motif, AxLyCxL is perfectly conserved in all studied sequences of vertebrates. Using in situ hybridization, we observed that myomixer was highly expressed in the embryonic myotome, particularly in the hyperplasic area. Moreover, myomixer remained readily expressed in white muscle of juvenile (1 and 20 g) although its expression decreased in mature fish. We also showed that myomixer is up-regulated during muscle regeneration and in vitro myoblasts fusion. Together, these data indicate that myomixer expression is consistently associated with the formation of new myofibers during somitogenesis, post-larval growth and muscle regeneration in trout.